Grinding operations



H. L FODMORE Dec. 5, we?

GRINDING OPERATIONS 2 Sheeis-Sheet Filed March 22, 1/965 HEW? A.

H. L. PODMORE Dec. 5, 1967 GRINDENG OPERATIONS 2 Sheets-Sheet FiledMarch 22, 1965 Inventor m w E R 0 w om PB L V: R N E H United StatesPatent 3,356,302 GRINDING OPERATIONS Henry Leveson Podmore, WetleyRocks, England, assignor to Podmore and Sons Limited and William BoultonLimited, jointly, Stalfordshire, England, both companies of EnglandFiled Mar. 22, 1965, Ser. No. 441,743 Claims priority, application GreatBritain, Apr. 6, 1964,

3 Claims. (Cl. 241-30) ABSTRACT OF THE DISCLOSURE The method ofgrinding, polishing and/0r deburring material to be processed includingplacing cylindrical pieces of treating media into a chamber along withthe material to be treated and subjecting the chamber to compoundvibrational movements to cause the media to orient into a generallyparallel rolling relationship.

Background of invention This invention relates to grinding operations inwhich the material to be processed, which may be either in the form of asuspension in liquid or as dry powder is fed into a chamber containingmedia of specific shape and subjected to controlled compound vibration.In vibration grinding mills at present in use the media is usuallyspherical giving a comparatively large volume of voids between thespheres and providing only point contact to effect the grindingoperation. It is found in practice that the volume of voids betweenspherical media approximates to 40% of the total volume of media andcharge. As a result of many experiments I have found the grindingefiiciency and the rate of grinding to be greatly enhanced if the volumeof voids between the media is substantially reduced. Since the use ofspheres as media must always leave a large volume of voids experimentshave been conducted upon other shapes and in particular upon cylindricalmedia. Generally cylindrical media were found to be inferior to spheresin that a random arrangement of the cylindrical pieces results in astill higher proportion of voids. Moreover the vibration of the millsubjected the cylindrical media to a succession of point impacts whichsoon caused the cylinders to wear down at the ends with the result thatthey became rounded and eventually the media tended to become spherical.The rate of wear on the media should of course be reduced to a minimumto prevent excessive contamination of the product.

Summary of invention Further experiments have shown, however, that it ispossible to create a predetermined orientation of the pieces ofcylindrical grinding media with most beneficial results.

The present invention consists in the use of a grinding chambercontaining cylindrical pieces of grinding media which are made to orientthemselves into a generally parallel relationship so that a rolling orrubbing action in line or face contact is created between the adjacentcylindrical surfaces of the pieces of media under the vibrationalmovement of the grinding chamber.

This predetermined orientation of the cylindrical pieces of media canbest be achieved by subjecting the grinding chamber and its contents tocompound rotational vibrations about an approximately vertical axis. Thetwo or more vibratory systems must be capable of phase adjustment andcontrol so as to produce and maintain near optimum packing density forthe media and charge of process material.

Under these conditions cylindricals will pack to give voidsapproximating to 22% of the total volume. It will be appreciated thatwhile a lower percentage of voids could be obtained by the use of mediain certain other shapes such as prisms and even cubes with roundededges, in practice the use of such media is found detrimental to rapidfeeding and discharge of the mills and also gives a low flow ratethrough the mills when used in continuous grinding processes.

The purpose of the phased compound vibratory system is to provideconditions which will facilitate free rotation of the pieces of mediawhich are not aligned but which will not disturb the alignment of thosepieces which are packed to give maximum packing density. Under suchconditions and after a sufficient interval of time, all the media willbe aligned to give the optimum packing density and will then provideline and face contact but no point contact.

The invention will be further described with reference to theaccompanying drawings in which:

FIGURE 1 is a side elevation of a grinding mill.

FIGURE 2. is a plan.

FIGURE 3 is a vertical section.

FIGURE 4 is a perspective view showing the grouping of the grindingmedia desired, drawn to a larger scale.

It is preferable that the grinding chamber 10 should be of cylindricalshape with its axis approximately vertical. For instance the grindingchamber may include an outer cylindrical wall 10* and an innercylindrical wall 10 both concentric about a vertical axis, so that asviewed in plan the chamber is of annular shape. Parallel alignment ofthe grinding media is facilitate by having the base 11 of the grindingchamber in the shape of a semi toroid.

If at any time the annular chamber 10 as a whole is rapidly displaced inthe direction of the arrow A, FIGURE 2, by a high frequency rotationalvibration about the vertical axis then the media at point B will besubjected to a pressure above that of the mean and the media at thepoint C will be subjected to a pressure below that of the mean. Now ifat the same time a second form of vibration is introduced which willimpart a small turning movement to the media, then provided the releaseof pressure at point C is adequate the media will rotate into a newposition. It will be appreciated that once the cylindrical media M,FIGURE 4 is packed to give maximum density as shown then the degree ofpressure reduction required to facilitate rotation of the cylindricalpieces of media is considerably greater than is necessary to produceparallel alignment and hence it the amplitude is correctly adjustedaligned media will remain so aligned.

The annular grinding chamber, in conjunction with the type of vibratoryaction referred to, is calculated to promote a circulation of the mediaaround the grinding chamber, but without upsetting the prescribedorientation of the media as a whole.

In the construction illustrated grinding chamber 10 is mounted on anannular series of springs 12 carried by a base 13 and is subjected tothe necessary compound vibrations by means of out-of-balance masses 14carried by a vertical spindle 15 mounted on the vertical axis of thegrinding chamber and subjected to rotation by an electric motor 16giving the high frequency compound vibration having the desiredrotational and upward and downward component; the angle of lead betweenthe two weights 14 being capable of adjustment so as to correctly phasethe two vibratory systems.

The term grinding is used herein broadly to include polishing orde-burring operations.

I claim:

1. Method of grinding and similar operations comprising the steps ofplacing cylindrical pieces of grinding media into a grinding chamber,feeding the material to be treated in the chamber, subjecting thegrinding chamher to controled compound vibrational movements, therebycausing the grinding media to orient into a generally parallelrelationship, and thus creating rolling and rubbing action in contactbetween adjacent surfaces of the pieces of media.

2. Method as claimed in claim 1 in which the material fed in is in theform of a suspension in liquid.

3. Method as claimed in claim 1 in which the material fed in is in a drystate.

References Cited UNITED STATES PATENTS Podmore et al. 241-30 Weston24130 Smith 241-30 Moore 241-30 WILLIAM W. DYER, JR., Primary Examiner.

10 H. F. PEPPER, Examiner.

W. D. BRAY, Assistant Examiner.

1. METHOD OF GRINDING AND SIMILAR OPERATIONS COMPRISING THE STEPS OFPLACING CYLINDRICAL PIECES OF GRINDING MEDIA INTO A GRINDING CHAMBER,FEEDING THE MATERIAL TO BE TREATED IN THE CHAMBER, SUBJECTING THEGRINDING CHAMBER TO CONTROLED COMPOUND VIBRATIONAL MOVEMENTS, THEREBYCAUSING THE GRINDING MEDIA TO ORIENT INTO A GENERALLY PARALLELRELATIONSHIP, AND THUS CREATING ROLLING AND RUBBING ACTION IN CONTACTBETWEEN ADJACENT SURFACES OF THE PIECES OF MEDIA.